1. Field of the Invention
The present invention relates to water repellant coating compositions, coatings made from the coating compositions, products coated by the coatings, and methods for making the same.
2. Background
Construction materials based on cellulosic and masonry substrates can be subject to damage by moisture after being exposed to the exterior environment. For example, moisture penetration into wood substrates can cause these materials to expand, widening cracks and finally causing deterioration to the structure of the panel due to volume changes resulting from water freezing and thawing during winter and summer months. In addition, water is essential for microbial attack (i.e., fungi, moss, lichen, etc.). Moisture content of 20% or greater in the wood can accelerate the breakdown of wood substrates. Masonry substrates can suffer the same type of degradation due to freeze/thaw resulting in what is known as sprawling and cracking.
Water repellant compositions for cellulosic materials, such as wood substrates, masonry substrates, and other substrates, are well known. The protection of substrates made of such types of materials initially used organic polymers (such as linseed oil) which were thought to protect the substrate from water. Advances in organic polymer synthesis pushed the technology to more crosslinkable polymers such as alkyds and acrylic technologies.
The addition of wax was thought to aid in water repellency due to increased beading on the substrate; however this protection tends to typically be short term when these substrates are placed in the presence of UV light, heat and moisture.
The modification of organic polymers with silicone is a way of extending durability by increasing hydrophobicity over a longer period of time. The high energy Si—O—Si bond on silicone makes it resistant to UV light and heat associated with exterior exposure. The low surface energy and increased hydrophobic surface make silicone ideal for increasing water repellency. Typical silicone polymers have a tendency to migrate to the surface of organic based coatings and wear away.
Silicone polymers which have non- or low reactivity or are based on a high dimethyl content tend to have a propensity to separate. The modification of the silicone/silane with organic substituents such as C3-C8 or phenyl type are more compatible with organic polymers and are less likely to migrate. The use of monomeric materials such as silanes have been used in the past with high alkoxy contents. These materials work well for increasing water repellency, however due to the alkoxy content they have an increased VOC which make them more difficult to use.
Different states have adopted regulations such as South Coast Air Quality Management District (SCAQMD) Rule 1113, which are more aggressive at reducing VOC than EPA regulations. It would be desirable to proved waterborne, low VOC, water repellents for cellulosic and masonry substrates, as well as other substrates, which meet and exceed these regulations.